Friday, May 24, 2013

Chasing Galileo's Sunspots

After doing the animation in the previous post, I found myself struck by the amount of detail Galileo put into his drawings, and how they compare to modern observations. His contentious contemporary, Christoph Scheiner, came up with not only better equipment for solar observations (including what can only be described as one of the first equatorial mounts), he also developed methods that would be used for more than a century, and which in evolved form still exists, but Galileo's drawings still look better. The information supplied from the Galileo project at Rice University's website indicate that the drawings that Galileo did of the Sun were around 150-152mm  123 - 125mm in diameter, about  6 " 5". We can only guess which telescope he used (he may have even used one purpose built), but it is certain that it was a Galilean in optical design.
The question, however, is what method did he use? We know that he used solar projection, but what did his setup look like? Here, things become vague. How did he aim the telescope? There are plenty of questions that remain about how he did it.
A few years back, I built a facsimile of one of Galileo's telescopes, and in theory it would be fine for this little experiment in historical astronomy. Instead, I am using the one modern telescope that is most like a Galilean in performance, a nearly fifty year old Tasco 40mm terrestrial telescope. As an astronomical instrument, it is extremely limited. In fact, as a terrestrial telescope it is extremely limited as well, possessing a narrow field and a somewhat dark field of view. That performance is very close to the performance of my long tube Galilean facsimile, in a shorter, easier to handle telescope.
Over the next few days and weeks, I will test out these methods using that old instrument and will, as always, share the results here.
(Edit - The diameters that were initially listed were incorrect; they have been corrected. R.L.)

No comments: